Filtered air breathing zone

ABSTRACT

A highly portable, localized filtered air breathing zone for a patient suffering from those respiratory diseases or who require protection from air borne contamination. The filtered air in which essentially all particulate matter has been removed provides a gaseous envelope in the breathing zone adjacent the top portion of the patient&#39;&#39;s bed. In another embodiment, the apparatus is arranged as to extend longitudinally of the bed and thus provide a patient zone extending transversely across the bed for essentially its entire length. The latter modification is to provide an essentially contamination free patient zone or breathing zone for intensive care units and for enclosures for small children requiring contamination free air. The patient zone is isolated from ambient air by means of three gas patterns, one formed at either vertical edge of the patient zone and one formed transversely across the top of the patient zone. These act as relatively high velocity air curtains and thus shield the center portion of the patient zone from the surrounding ambient air. A gas pervious diffusion wall is provided in the apparatus between the areas defined by the three high velocity gas patterns. This forms the center portion of the patient zone and provides a positive method for filling the breathing zone with contamination free filtered air. All of the air circulated is taken from a purified or filtered air source preferably derived by impelling ambient air through a high efficiency filter.

United States Patent [191 Wood Primary Examiner-Dennis E. Talbert, Jr.Att0rneyWilliam R. Price [57] ABSTRACT A highly portable, localizedfiltered air breathing zone for apatient suffering from thoserespiratory diseases or who require protection from air bornecontamination. The filtered air in which essentially all particulatematter has been removed provides a gaseous envelope in the breathingzone adjacent the top portion of the patient's bed. In anotherembodiment, the apparatus is arranged as to extend longitudinally of thebed and thus provide a patient zone extending transversely across thebed for essentially its entire length. The latter modification is toprovide an essentially contamination free patient zone or breathing zonefor intensive care units and for enclosures for small children requiringcontamination free air. The patient zone is isolated from ambient air bymeans of three gas patterns, one formed at either vertical edge of thepatient zone and one formed transversely across the top of the patientzone. These act as relatively high velocity air curtains and thus shieldthe center portion of the patient zone from the surrounding ambient air.A gas pervious diffusion wall is provided in the apparatus between theareas defined by the three high velocity gas patterns. This forms thecenter portion of the patient zone and provides a positive method forfilling the breathing zone with contamination free filtered air. All ofthe air circulated is taken from a purified or filtered air sourcepreferably derived by impelling ambient air through a high efficiencyfilter.

PATENTEDAPR 3 I973 INVENTOR.

SHEET 1 BF FIG-l F lG-Z W BRUCE W000 BY k4. Wi

ATTORNEY PATENTEDAPR3 1975 SHEET 2 OF 3 FIG 4 INVENTOR.

W BRUCE W000 BY M MW [1111/ 1/1 1 I 111 IIIIIIIIIIIIIIII I I III/Ilil/ATTORNEY PATENIEDAPH 1975 3,724,172 sum 3 or E3 FIG-5 INVENTOR.

WBRucE WOOD ATTORNEY FILTERED AIR BREATHING ZONE BACKGROUND OF THEINVENTION This invention relates to the provision of a gaseously formedcurtain and is particularly applicable to the provision of an aircurtain so located as to isolate air in a given space from thesurrounding ambient air. More specifically the invention relates to anapparatus and method for controlling the environment in a localized zoneand more particularly for effectively and economically isolating apatient zone or a breathing zone from the external environmental.

DESCRIPTION OF THE PRIOR ART Patients in intensive care units whethersuffering from respiratory infection, extensive burns or patients undergoing preor post-operative care for relatively severe or extensiveoperations are particularly subject to pathogenic micro organisms. Crosscontamination, even in the most efficiently run hospitals has continuedto exist despite improved aseptic techniques and antibiotics. It isknown that if the air in the vicinity of a patient during preandpost-operative periods is maintained virtually free from pathogenicorganisms, the incidence of infection is only a fraction of thatexisting under normally-controlled air conditions. Previously, patientshave been isolated from the bacteria and virous laden air by thephysical isolation of a specific part or even the whole of the patientwithin a plastic envelope or enclosure into which is pumped clean,contamination free air. However, patient morale is adversely affected'by total confinement created by the severe claustrophobic environmentof a plastic. tent. Further, nursing care is complicated since directphysical treatment must be carried out through closed ports or air lockswhich demand considerable patience and training of hospital personnel.

To overcome these severe disadvantages, apparatus has been proposedwhich leaves one or more walls open and isolated from the externalatmosphere by reason of an air curtain. Such apparatuses, are disclosedand claimed by Denny in U.S. Pat. No. 3,462,920, in 1969 and by Truhanin US. Pat. No. 3,511,162, in 1970. Both of these, however, aredependent upon a rather elaborate and expensive superstructurecomprising a plenum chamber located parallel to the mattress of thepatients bed and containing a series of ports or nozzles directeddownwardly onto the patient with high velocity gas curtains on theperipheral edges of the plenum to isolate the filtered gaseousenvironment surrounding the patient from the bacteria ladened ambientair. Truhan additionally provides for recycling of the filtered airthrough a return duct 17 wherein the air forming the curtain and thepatient zone is recycled to filtering media to be reused in isolatingthe patient zone.

The use of horizontal air flow in hospital applications requiringcontamination free breathing areas has been accomplished in the past byinstalling a bank of filters either at the head or along the side of thebed and bathing the patient with filtered air flows of from 90 to 100feet per minute. These installations have involved a complete wallfabricated of high efficiency particulate air filter (I-IEPA) modules.Each module might be 2 feet in width and up to 8 feet in height. Theinstallations require an area of at least 3 to 4 feet behind the filtermodule bank to service the filters. The cost of these units is extremelyhigh and the rate of air flow can be a problem to some patients. Theunits are not portable.

SUMMARY OF THE INVENTION The present invention provides a highlyportable unit for protecting vulnerable patients from air borne bacteriaand viral and other irritating solid particulate contamination. Further,the present invention provides a relatively inexpensive unit forprotecting only the breathing zone of patients requiring protection fromair borne contamination. The present invention provides a relativelyinexpensive and portable unit for protecting a vulnerable patient eitherfrom bacteria, viral or particulate contamination so as to isolate thebreathing zone of the patient from contaminated external atmosphere andyet provide easy access of the patient to nursing and medical personnel.In contrast to installations presently in use involving an entire bankof filter modules, a small compact HEPA filter, as for example, one 12inches in height and 12 inches in depth can be used with a high rate ofair flow through the filter. Thereafter the filtered air is diffused soas to flow at relatively low rates into the patient or breathing zone.By contrast with other developments the present invention does notdirect the air curtain downwardly onto the patient but provides an aircurtain having three borders of rather high velocity air which projectin a generally horizontal direction to define the top and sides of thepatient zone. The center portion of the patient zone is provided by arelatively low velocity air pattern obtained through a pervious gasdiffusion wall. This in a preferred embodiment involves a velocitygradient across said gas pattern. The velocity is lowest at the centerof the gas pattern and increases gradually toward the lateral edges ofthe breathing zone. While the unit is primarily adapted for use inproviding a patient or breathing zone near the pillow or top area of thepatients mattress, and is designed for use by patients requiringprotection from air borne particulate contamination, it is within thescope of this invention to utilize the apparatus so as to extend alongthe length of one side of the patients 'bed so that the patient zoneformed by the high velocity gas patterns extend horizontally across thepatients mattress for virtually the entire length of the bed. Thus,there is provided in this modification a patient zone comprising anenvelope of purified air physically isolated from bacteria Iadened andenvironmental air and encompassing essentially the entire area of thepatients mattress. Further it is within the scope of this invention toprovide a unit adapted for a chair for use with ambulatory patients whorequire a contamination free breathing zone. Because of the novel andrelatively low cost construction of the apparatus of this invention, aneffective patient zone is provided, isolated from the externalenvironment by use of relatively low velocity air. Thus the patient isnot subject to drafts, noise is essentially eliminated and there is noclaustrophobic effect. The patient is instantly accessible to medicaland surgical care from the top side or front of the patient zone.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation with partsin section of the device of this invention in use with a bed and whichillustrates in dotted lines the patient breathing zone as well asportions of the invention when in tilted position. FIG. 2 is afragmentary plan view illustrating in dotted lines the outer boundary ofthe patient or breathing area.

FIG. 3 is a sectional view taken along lines 3-3 of FIG. l'whichillustrates the relation of the plenum chamber, the ports and gaspervious wall forming the 1 front face of the plenum chamber.

FIG. 4 is a sectional view along lines 44 of FIG. 3 illustrating thestructure of the various diffusion members of the gas per viousdiffusion wall and illustrating the direction of air flow through theplenum chamber.

FIG. 5 is a view in perspective illustrating the apparatus of thisinvention extending longitudinally over a bed to protect the entiremattress area for use as an intensive care unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. I atypical hospital bed 1, including a mattress 2 is shown in full lines.Behind the bed is a blower and filter package 4 and duct 5 whichconnects to the plenum headboard to distribute air into the breathing orpatient zone 7. It will noted in FIG. 1 that canopy 11 extends forwardlyfrom the plenum headboard and side shield members 12 extend diagonallyfrom the forward edge of canopy to the plenum headboard 10 at aboutmattress level. It is well known that hospital beds are pivoted so as toallow the patient to adjust the mattress to sitting, reclining orsleeping positions. This is shown in dotted lines in the FIG. 1 showingthat the relationship of the headboard l0 and the canopy 11 relative tothe top portion of the mattress remains constant even though the angulardisposition of the mattress changes in well "known manner. Thefragmentary plan view illustrated in FIG. 2 illustrates the outerboundary of the patient zone 7 relative to the canopy 11.

Referring now to FIG. 1, air is pulled into thefilter blower package 4through air intake (not shown). Contained in the filter blower package 4is a blower or gas impeller and a high efficiency filter. Such highefficiency particulate air (HEPA) filters are well known in the art andhave been shown to remove 99.97 to 99.99 of all particles and bacteria,0.3 microns in diameter and larger. Smaller particles are also removedby this type of filter but the amount of removal of these particles hasnot been established. Removal of smaller particles is not a matter forsignificant concern, however, since most bacteria range from 0.5 to 25microns in diameter and very rarely exist in the air as singleunattached cells but are usually attached to particles of dust and skinscales considerably larger than themselves. Typical diameters forparticulate matter includes the following:

pelled through duct 5 to the plenum headboard 10. It is directed by theV shape air directing vanes 25 and by the median air directing vane 26to the upper portions of the plenum chamber 24. At the forward part ofthe canopy 11 is a horizontal port means 15 formed by the canopy l1 andthe lower closure member 16 to form an elongated slit horizontallydisposed relative to the mattress 2 and extending transversely acrossthe mattress.

High velocity air issuing from this horizontal port forms an air patternwhich direction of flow is parallel to the top of the mattress 2 andwhich has its long axis directed transversely across the mattress. Theside ports 17 are made up of a series of jet openings 18 which arevertically aligned along the side edges of the plenum chamber 24. Thusthe air pattern formed by high velocity air issuing in horizontaldirection along the length of the mattress 2 may be consideredrectangular. In any event, when viewed in section relative to thedirection of flow the longitudinal axis of the air pattern is verticaland forms the lateral edges of the patient breathing zone 7.

The pervious diffusion wall 20 (which is defined by the sideport means17 and the horizontal port means 15) comprises a perforated diffusioncloth media 21 covering a supporting wire screen 22 and a perforatedaluminum plate 23 containing about 43 percent openings. The gas patternformed through the pervious diffusion wall varies from 10 PPM (feet perminute) in the center to 40 to 50 FPM along the vertical edge.

The variation in exit velocity from the pervious diffusion wall 20 isaccomplished by gas directional vanes such as 25 and 26 and by themanipulation of nonporous blanking material over the diffusion media 21to direct the air flow to vertical edges as required. The lowestvelocity gases are in the pillow area and the higher velocity gasesgradually increase as the pattern approaches the lateral edges adjacentto the side port means 17.

As previously mentioned, the primary purpose of this invention is forpatients suffering from respiratory illness, such as asthma.Nevertheless, it is within the scope of this invention to arrange theplenum chamber 10 and the canopy 11 and the side shields 12 so that theunit extends longitudinally from head to foot of a patients bed so thatthe (filtered air) zone extends across the entire mattress.

Referring now to FIG. 3, it has been found that in order to maintain theintegrity of the air curtains or air patterns that the velocity of theissuing from the side port means 17 and from the top horizontal portmeans 15 should be in the range of I00 to 200 feet per minute with atotal of about 300 CF M of filtered air exhausting from all outlets inheadboard 10.

Good results have been obtained by utilizing /4 inch diameter jetopenings 18 spaced 1 inch on center in side port 17 with the top 25percent of the holes blocked off. Further, the jet openings 19,supplying horizontal slot 15 are one-fourth inch in diameter locatedone-half on centers with every third opening closed. Air velocity canalso be regulated by increasing or decreasing fan speeds; opening orclosing the jet openings 18 or 19 or by other techniques known to theart.

The effectiveness of the invention is well demonstrated by test datameasuring the integrity of the 81,000 particles 0.5 microns or larger18,000 1.0

These measurements were made using a Baush and Lomb Counter (40-1 withdigital readout.

The test measurements of the contamination level surrounding the openend of the breathing zone 7 were taken by establishing an imaginary gridparallel to the pervious diffusion wall 20 and taking a reading everyinch in the vertical and horizontal planes. The grid was first taken oneinch from the outer most edge and gradually moved away from the face ofdiffusion wall 20. It was determined that the high velocity jet actionof the horizontal air pattern from part prevented 0.5 micron and largerparticles from entering the breathing zone 7 for almost the full heightof the diffusion wall as far as 20 inches downstream from plate 23 alongthe centerline of the bed. However, as the grid was moved away from thewall 20 particulate matter started to penetrate the vertical airpatterns formed by side ports 17 on each side of the bed. The followingmeasurements were taken in the grid plane 17 inches down from the wall20. (These figures were chosen since 17 inches provides a more thanample breathing zone for the patient.) All the readings were zero in azone extending from 2 inches below the top edge of canopy 11 from thecenter of mattress to 3 inches from the side edge of the bed. Allreadings 4 inches from the edge ofv the bed, in an area extendingvertically from canopy to 3 inches above the mattress, were zero exceptfor 1 which read 100 particles of a size 0.5 microns and larger. At aheight of 3 inches above the mattress particle counts for 0.5 micronsdiameter particles of 300 to 900 per cubic foot were obtained at thelateral border 8 inches from the edge of the bed. The particle count atmattress level .is believed to result from particles shed from thesheet. It should be that the particle counts at 3 inches from the edgeof the bed averaged 800 which is far below the ambient level of 81,000particles per cubic foot.

The same procedure was followed testing for particles having diametersof 2 microns and larger and it was determined that 24 inches downstreamfrom the perforated plate 23, a zero count was found. This zone extendedfrom 2 inches below the canopy to the top of the mattress with noreading at 1 inch above the mattress. The zone defined by the airpatterns, produced by side port 17 and top port 15 are such that theentire center area of the patient breathing zone 7 is essentiallycompletely free of particles of 0.5 micron diameter or above, at adistance of 17 inches from the headboard l0 and completely free of 2micron and larger particles at a distance of 24 inches from theheadboard 10. Therefore, as previously indicated, essentially allpathogenic organisms will be shielded from a zone extending from 1 to 17inches away from the headboard and basically all bacteria, pollen andsp'ores will be shielded from the breathing zone, extending for adistance of from 1 to 24 inches, from the headboard 10.

In other words the contamination free zone for 0.5 micron diametermaterial is 7 inches shorter than the zone for 2 micron diametermaterial, but in any event is more than ample as a breathing zone for apatient. All of the experiments were run with a side shield 12 in placebut without a closure member similar to closure member 16 to direct theair. It was found, however, that it was necessary to extend closuremember 16 for 10 inches from the perforated plate 23 to be effective.The canopy 11 extended 14 inches forwardly of headboard 10 while, aspreviously indicated, the effective contamination free breathing area 7extended forwardly from 17 to 24 inches.

It is clear, that by providing a canopy 11 with a forwardly extendinghorizontally disposed port 15 near the forward edge of the canopy andproviding port means at the forward edge of the side shields 12 that theeffective zone of the mattress could be extended so that when the unitis disposed longitudinally the entire mattress could be isolated fromthe surrounding environment. Of course, it is also possible to increasethe velocity of gases extending from the port means to extend thebreathing zone.

By utilization of the relatively low velocity of purified gases the unitruns quietly, drafts are essentially eliminated and the cost of the unitand operating expenses are relatively low.

Many modifications will occur to those skilled in the art from thedetailed description here in above given and such modifications aremeant to be exemplery in nature and non-limiting except so as to becommensurate in scope with the appended claims.

I claim:

1. Apparatus for providing a filtered gaseous envelope of air forisolating a patient zone from an ambient environmental gaseous mediumwhich comprises: a filtering means, a passage means in communicationwith said filtering means and said patient zone and a motor driven gasimpeller for impelling air through said filtering means and through saidpassage means;

A. the improvement which comprises:

1. a vertically disposed wall positioned adjacent to said patient zone,the front face of said wall defining a side of said patient zone;

2. a gas pattern forming means in communication with said passage meanswhich comprises:

a. a pair of spaced port means each being vertically disposed relativeto said front face of said wall and each being located in alignment withone or the other of the lateral edges of said front face for providingstreams of relatively high velocity air to form the lateral borders ofsaid patient zone;

. a canopy extending forwardly over a portion of said patient zone andextending across the top of said wall;

. a horizontally disposedport means opening near the forward edge ofsaid. canopy for providing a stream of relatively high velocity air toform the upper border of said patient zone; and

. a low velocity pervious diffusion wall located within the area definedby said canopy and said vertically disposed port means for producing astream of low velocity air to form a zone embodying the center portionof said patient zone.

2. Apparatus, as defined in claim 1, in which said vertically disposedwall is the headboard for a patients bed.

3. Apparatus, as defined in claim 2, in which said headboard contains aplenum chamber in communication with said passage means and with saidpatient 7 zone.

4. Apparatus, as defined in claim 1, the further combination with saidpassage means of:

A. a plenum chamber and B. air directing vanes to direct the highvelocity air to said port means and said low velocity air to said lowvelocity pervious diffusion wall.

5. Apparatus, as defined in claim 1, the further combination therewithof A. plenum chamber and B. air directing vanes to direct highervelocity air to the sides of said low velocity pervious wall and lowervelocity air to the center of said low velocity perviouswall so as toform a zone of air of variable velocity said zone having a relativelylow velocity in its center and a velocity which increases toward itssides.

6. Apparatus, as defined in claim 1, in which said spaced port meanscomprises a series of gas outlet openings arranged in verticalalignment.

7. Apparatus, as defined in claim 1, the further combination therewithof a pair of gas impervious side shields extending from the ends of saidwall forwardly to cover a portion of the lateral edges of said patientzone. 1

8. Apparatus, as defined in claim 7, in which said port means comprisesa nozzle formed by such shield.

9. Apparatus, as defined in claim 8, in which said nozzle is formed bysaid shield and by a cooperating vertically disposed closure member toform a vertically oriented elongated slit. 1

10. Apparatus, as defined in claim 1, in which said horizontallydisposed port means comprises a nozzle formed by said canopy near itsforward edge.

11. Apparatus, as defined in claim 10, in which said nozzle is formed bysaid canopy and by a cooperating lower closuremember to form anelongated slit which extends across said patient zone.

12. Apparatus, as defined in claim 1, in which said pervious diffusionwall is a gas diffusion means.

13. Apparatus, as defined in claim 3, in which said pervious diffusionwall is in communication with said plenum chamber.

14. Apparatus, as defined in claim 13, in which said pervious diffusionwall includes a diffusing media stretched over said wall.

15. The process of providing a filtered gaseous envelope of air toisolate a patient zone from-an environders of said patient zone; 1. eachof said gas patterns when viewed in cross section relative to thedirection of flow having a long major axis and a narrow minor axis inwhich said major axis is vertically disposed;

C. shielding a portion of the top of said patient zone with a forwardlyprojecting canopy means,

D. forming a third high velocity gas pattern of air near the forwardedge of said canopy means by projecting filtered air forwardly of saidcanopy means so that its direction of flow is in a horizontal plane so'as to form the top border of said patient zone,

1. said third gas pattern when viewed in cross section relative to thedirection of flow having along major axis extending horizontally acrosssaid patient zone,

E. forming a fourth rectangular gas pattern of filtered air ofrelatively low velocity within the area defined by said first, secondand third pattern, said fourth gas pattern when viewed in cross sectionrelative to its direction of flow having a long major axis horizontallydisposed and a relatively wide minor axis vertically disposed, saidfourth gas pattern forming the breathing portion of said patient zone,

i 16. The process, as defined in claim 15, in which said source of airis provided by impelling ambient air through a high efficiency filteringmeans and thereafter impelling said filtered air to said patient zone.

17. The processes as defined in claim 16, the further step whichincludes:

A. impelling, said filtered air against air directing vanes so as toincrease the velocity of the filtered air going to form the said firstand second air pattern.

18. The process as defined in claim 16, the further step whichcomprises:

A. impelling said filtered air against air directing vanes so as toincrease the velocity of filtered air going to form said third gaspattern.

- 19. The process as defined in claim 16, the further step-whichcomprises:

A. impelling said filtered air against air directing vanes so as toincrease the velocity of air toward the lateral edges of said fourth gaspattern so as to form a velocity gradient across said gas pattern, saidvelocity being lowest at the center of the gas pattern and increasingtoward its lateral edges.

2. Apparatus, as defined in claim 1, in which said vertically disposedwall is the headboard for a patients bed.
 2. a gas pattern forming meansin communication with said passage means which comprises: a. a pair ofspaced port means each being vertically disposed relative to said frontface of said wall and each being located in alignment with one or theother of the lateral edges of said front face for providing streams ofrelatively high velocity air to form the lateral borders of said patientzone; b. a canopy extending forwardly over a portion of said patientzone and extending across the top of said wall; c. a horizontallydisposed port means opening near the forward edge of said canopy forproviding a stream of relatively high velocity air to form the upperborder of said patient zone; and d. a low velocity pervious diffusionwall located within the area defined by said canopy and said verticallydisposed port means for producing a stream of low velocity air to form azone embodying the center portion of said patient zone.
 3. Apparatus, asdefined in claim 2, in which said headboard contains a plenum chamber incommunication with said passage means and with said patient zone. 4.Apparatus, as defined in claim 1, the further combination with saidpassage means of: A. a plenum chamber and B. air directing vanes todirect the high velocity air to said port means and said low velocityair to said low velocity pervious diffusion wall.
 5. Apparatus, asdefined in claim 1, the further combination therewith of A. plenumchamber and B. air directing vanes to direct higher velocity air to thesides of said low velocity pervious wall and lower velocity air to thecenter of said low velocity pervious wall so as to form a zone of air ofvariable velocity said zone having a relatively low velocity in itscenter and a velocity which increases toward its sides.
 6. Apparatus, asdefined in claim 1, in which said spaced port means comprises a seriesof gas outlet openings arranged in vertical alignment.
 7. Apparatus, asdefined in claim 1, the further combination therewith of a pair of gasimpervious side shields extending from the ends of said wall forwardlyto cover a portion of the lateral edges of said patient zone. 8.Apparatus, as defined in claim 7, in which said port means comprises anozzle formed by such shield.
 9. Apparatus, as defined in claim 8, inwhich said nozzle is formed by said shield and by a cooperatingverticaLly disposed closure member to form a vertically orientedelongated slit.
 10. Apparatus, as defined in claim 1, in which saidhorizontally disposed port means comprises a nozzle formed by saidcanopy near its forward edge.
 11. Apparatus, as defined in claim 10, inwhich said nozzle is formed by said canopy and by a cooperating lowerclosure member to form an elongated slit which extends across saidpatient zone.
 12. Apparatus, as defined in claim 1, in which saidpervious diffusion wall is a gas diffusion means.
 13. Apparatus, asdefined in claim 3, in which said pervious diffusion wall is incommunication with said plenum chamber.
 14. Apparatus, as defined inclaim 13, in which said pervious diffusion wall includes a diffusingmedia stretched over said wall.
 15. The process of providing a filteredgaseous envelope of air to isolate a patient zone from an environmentalambient gaseous medium, which comprises the steps of: A. providing asource of filtered air; B. forming a first and second relatively highvelocity rectangular gas pattern by projecting filtered air so that thedirection of flow of each of said gas patterns project horizontally toform the lateral borders of said patient zone;
 16. The process, asdefined in claim 15, in which said source of air is provided byimpelling ambient air through a high efficiency filtering means andthereafter impelling said filtered air to said patient zone.
 17. Theprocesses as defined in claim 16, the further step which includes: A.impelling, said filtered air against air directing vanes so as toincrease the velocity of the filtered air going to form the said firstand second air pattern.
 18. The process as defined in claim 16, thefurther step which comprises: A. impelling said filtered air against airdirecting vanes so as to increase the velocity of filtered air going toform said third gas pattern.
 19. The process as defined in claim 16, thefurther step which comprises: A. impelling said filtered air against airdirecting vanes so as to increase the velocity of air toward the lateraledges of said fourth gas pattern so as to form a velocity gradientacross said gas pattern, said velocity being lowest at the center of thegas pattern and increasing toward its lateral edges.